1. Field of the Invention
The present invention relates to an optical connector, such as an Angle-Pc connector, for connecting the slanted, polished surfaces of optical fibers together.
2. Description of the Related Art
As an optical connector, for use in optical communications or the like, a conventional Angle-Pc (Physical Contact) connector is used for the purpose of reducing connection loss and reflection return light at the connection of connectors, which has an optical fiber held in the ferrule and polished, at its end face together with an end face of the ferrule end face, oblique relative to a plane vertical to the axis of the optical fiber and into a convex spherical surface.
Herein, the ferrule to be used in the conventional Angle-PC connector is explained.
FIGS. 16A-16C perspective and plan views of a ferrule according to the related art.
As shown in FIGS. 16A-16C, a ferrule 160 used in an Angle-PC connector comprises a ferrule cylindrical body 140 having a tip face having a circular cylinder form provided as a convex surface form slanted relative to a plane orthogonal to the axis, and a flange member 150 fit in a rear end of the ferrule cylindrical body 140. The flange member 150 has a flange part 153 radially projecting and circumferentially extending on the outer periphery thereof close to the ferrule cylinder 140. The flange part 153 is provided with a key groove 154 which, when held in a not-shown plug frame of the Angle-PC connector, is to be engaged with the engaging projection axially provided in the same engaging width in the plug frame. The key grooves 154 are axially provided equal in width, in four locations at an interval of 90 degrees with respect to a circumferential direction of the flange part.
Such ferrules, held in plug frames, are to be optically connected at a low insertion loss and high return loss through an optical connector adapter or the like, by making an opposed connection with the end surfaces of the ferrules 160 placed in abutment against each other.
However, in the Angle-PC connector, there is a problem that, in case the ferrule has a great movement in rotational direction about the axis, the convex spherical surface is increased in eccentric center of curvature, thus making impossible to realize a low insertion loss and high return loss.
In this manner, in order to realize a low insertion loss and high return loss, there is a need to provide an eccentric center of curvature of 50 μm or less to the spherical surface provided at the tip surface of the ferrule cylindrical body. This requires to suppress the rotation angle of the ferrule in rotational direction about axis to ±2 degrees or less, preferably ±3 degrees or less.
For this reason, by providing 0.01-0.1 mm to a clearance between the flange-part key groove of the flange member and the engaging projection provided in the plug frame, the rotation chatter of the ferrule about the axis can be suppressed low to provide an eccentric center of curvature of 50 μm or less thereby providing a low insertion loss and high return loss.
However, conventionally, in case to provide a clearance 0.01-0.1 mm to between the key groove of the flange member and the engaging projection in order to suppress the rotation chatter of the ferrule about the axis, the optical connector plug when attached/detached to/from the optical connector adapter is restricted in the radial movement of the ferrule, resulting a problem of poor attaching/detaching stability.
Meanwhile, as compared to the optical connector plug using a ferrule cylindrical body having an outer diameter of 2.5 mm, the optical connector plug in which the ferrule cylindrical body uses a 1.25-mm ferrule cylindrical body has a necessity to reduce generally to a half the clearance between the flange-part key groove and the engaging projection in suppressing low the eccentric center of curvature. This, however, involves a problem that accurate working is required, thus making not feasible substantially.